Companies in the video game industry and possibly other sectors have been targeted in attacks involving improved variants of the notorious PlugX remote access trojan (RAT).
Palo Alto Networks has spotted several interesting PlugX samples believed to have been used by the same threat actor. While the company has not provided any details on the actor behind these attacks, PlugX has often been used by China-linked threat groups.
The attacks start with a malicious Word document named “New Salary Structure 2017.doc,” which exploits CVE-2017-0199, an Office vulnerability that has been used by several threat actors, including ones linked to China and Iran.
The exploit downloads a Windows installer file and a PowerShell script that appears to be based on an open source Ruby exploitation library. Both files can load a shellcode designed to unpack the main PlugX DLL in memory. The shellcode is loaded only after the presence of a virtual environment is checked.
The PlugX samples analyzed by Palo Alto Networks contacted several Pastebin URLs containing the addresses of command and control (C&C) servers. The content is encoded via a technique that PlugX has been known to use.
Researchers have described these PlugX samples as “paranoid” due to the fact that the batch script responsible for executing the malware also attempts to clean up after itself by deleting all files created during installation and initial execution, registry keys, and UserAssist key entries.
“Clearly the attacker using this PlugX is paranoid about it being detected on disk, both in the registry and the file system. To top this off the script runs most of the deletion commands more than once,” experts said in a blog post. “The result is that there should be no evidence that the malware was ever executed on the disk, making it harder for forensics teams to identify how the malware got there, and meaning that memory or network based detection would be required to identify the intrusion.”
Researches noticed that, in the first half of this year, the developers of these “paranoid” samples also added mechanisms for bypassing application whitelisting techniques possibly used by their targets. They achieved this by using code made available on GitHub by a user named “SubTee” and, in some cases, they also added some custom code.
While Palo Alto Networks reported that these attacks appear to mainly target the video game industry, the company believes other types of organizations that are outside its telemetry may have been targeted as well.
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